Can't answer as regards to Silverseas and Regent as we have not tried them, but you might want to take a look at Azamara Club Cruises, part of RCCI have two 700 passenger ships and provide in our opinion a more upmarket experience without being at all stuffy. Prices are higher than say Celebrity but service is better, gratuities are included as are a good selection of drinks, you can pay to upgrade to a premium package but not really required unless you have a strong preference to certain brands. Dress code is resort casual so suits and ties are definitely not needed, but could be worn if you feel like it.
They have also had some reasonable deals recently such as free upgrades (inside to balcony) and free flights, so well worth a look.
Carol & John